The present invention relates to a process for preparing an amine-substituted thiourea dioxide by the reaction of thiourea dioxide and a primary amine.
Since thiourea dioxide exhibits a strong reducing ability in a basic aqueous solution it is in wide use as a reducing agent in the dyeing industry and camera industry.
Further, in the field of polymers and that of organic chemistry, it has been studied to use thiourea dioxide as a stabilizer for various compounds (e.g. U.S. Pat. Nos. 2,472,868 and 3,070,569), as an amino resin curing agent (e.g. German Patent No. 1,215,363 and French Patent No. 1,445,045), or as a vinyl monomer polymerization initiator wherein thiourea dioxide is used together with iron-hydrogen peroxide [e.g. Am. Dyest. Rep. 75, 26-34 (1986)]. Thiourea dioxide has come to be applied to these uses gradually.
In the field of high polymers and that of organic chemistry, however, the application range of thiourea dioxide is limited because thiourea dioxide is insoluble in most organic solvents other than water. In these fields there are only extremely limited examples of industrial use of thiourea dioxide.
On the other hand, as to the method of preparing derivatives of thiourea dioxide, there has been proposed a method wherein thiourea derivatives such as N,N'-diphenylthiourea, N,N'-dibenzylthiourea and N,N'-dicyclohexylthiourea are oxidized with hydrogen peroxide to prepare the corresponding thiourea dioxide derivatives, as described in J. Chem. Soc. Perkin II, 4, 1500 (1972) and Synth. Commun. 4, 389 (1974). But this method is of less industrial utility because it is difficult to obtain the starting thiourea derivatives industrially.
It is the object of the present invention to overcome the above-mentioned drawback of the prior art and provide a process for effectively preparing an amine-substituted thiourea dioxide of great utility value.
It is described, for example, in Angew. Chem., 67, 275 (1955) and Sci. Pharm., 51, 283 (1980) that when thiourea dioxide is reacted with amino group-containing compounds, there usually are produced derivatives of guanidine and of cyanamide through decomposition of thiourea dioxide. In those literatures there is not described at all the preparation of amine substituted products of thiourea dioxide as in the present invention by the said reaction.